[clang] [clang] fix runtime check listing types which can appear in a NestedNameSpecifier (PR #155272)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Matheus Izvekov (mizvekov)

<details>
<summary>Changes</summary>

Through alias templates, followed by canonicalization, any canonical dependent type can appear in a NestedNameSpecifier. Remove the list as a practical matter.

This fixes a regression reported here: https://github.com/llvm/llvm-project/pull/147835#issuecomment-3220455978

Since the regression was never released, there are no release notes.

---
Full diff: https://github.com/llvm/llvm-project/pull/155272.diff


2 Files Affected:

- (modified) clang/lib/Sema/TreeTransform.h (+3-14) 
- (modified) clang/test/SemaTemplate/nested-name-spec-template.cpp (+13-8) 


``````````diff
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 1d14ead778446..87550614f645b 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -5539,21 +5539,10 @@ QualType TreeTransform<Derived>::TransformTypeInObjectScope(
         TLB, TL.castAs<DependentNameTypeLoc>(), /*DeducedTSTContext=*/false,
         ObjectType, UnqualLookup);
   }
-  case TypeLoc::Typedef:
-  case TypeLoc::TemplateSpecialization:
-  case TypeLoc::SubstTemplateTypeParm:
-  case TypeLoc::SubstTemplateTypeParmPack:
-  case TypeLoc::PackIndexing:
-  case TypeLoc::Enum:
-  case TypeLoc::Record:
-  case TypeLoc::InjectedClassName:
-  case TypeLoc::TemplateTypeParm:
-  case TypeLoc::Decltype:
-  case TypeLoc::UnresolvedUsing:
-  case TypeLoc::Using:
-    return getDerived().TransformType(TLB, TL);
   default:
-    llvm_unreachable("unexpected type class");
+    // Any dependent canonical type can appear here, through type alias
+    // templates.
+    return getDerived().TransformType(TLB, TL);
   }
 }
 
diff --git a/clang/test/SemaTemplate/nested-name-spec-template.cpp b/clang/test/SemaTemplate/nested-name-spec-template.cpp
index 153f4e2555e3a..0f51a14af9e52 100644
--- a/clang/test/SemaTemplate/nested-name-spec-template.cpp
+++ b/clang/test/SemaTemplate/nested-name-spec-template.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -Wno-c++20-extensions
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c++98 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-c++11-extensions -std=c++98 %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
 
 namespace N {
@@ -24,14 +24,7 @@ namespace N {
 
   M::Promote<int>::type *ret_intptr3(int* ip) { return ip; }
   M::template Promote<int>::type *ret_intptr4(int* ip) { return ip; }
-#if __cplusplus <= 199711L
-  // expected-warning at -2 {{'template' keyword outside of a template}}
-#endif
-
   M::template Promote<int> pi;
-#if __cplusplus <= 199711L
-  // expected-warning at -2 {{'template' keyword outside of a template}}
-#endif
 }
 
 N::M::Promote<int>::type *ret_intptr5(int* ip) { return ip; }
@@ -181,3 +174,15 @@ namespace SubstTemplateTypeParmPackType {
   template void f<B>();
 } // namespace SubstTemplateTypeParmPackType
 #endif
+
+namespace DependentUnaryTransform {
+  template <class T> using decay_t = __decay(T);
+  template <class, class> struct A;
+  template <class T> struct A<T, typename decay_t<T>::X>;
+} // namespace DependentUnaryTransform
+
+namespace DependentSizedArray {
+  template <int V> using Z = int[V];
+  template <class, class> struct A;
+  template <class T> struct A<T, typename Z<T(0)>::X>;
+} // namespace DependentUnaryTransform

``````````

</details>


https://github.com/llvm/llvm-project/pull/155272